Drilling systems are used for drilling oil wells and carrying out geological boreholes. In the latter case often a sample of ground is collected in the form of a core extracted from the hole formed in the so-called coring operation. Such operations are sometimes performed in hardly accessible spots, or even in space. The drilling rig is then transported by a piloted or unmanned craft, a satellite or a lander. In these applications the key parameter of the drilling rig is its mass and power consumption, which have to be minimised.
In the case of drilling with casing tube, after extracting the output a tube is placed in the drilled hole. In ground conditions sometimes subsequent sections of the rigid tube are inserted into the borehole. In conditions of work performed from a vehicle this is difficult or even impossible. In the art is known the application of so-called curled strips for casing.
Curled strip tubes have numerous applications in devices adapted to change of length, which have to combine simultaneously small mass and high durability and high stiffness. This relates in particular to booms, manipulators and antennas used in aviation and space exploration. A tube made of elastic material, i.e. a material with a high yield strength, e.g. spring steel, which after straightening and winding on a drum has small size and mass. Being drawn it returns to its nominal form in which it was hardened. In this way, after unwinding the strip from the drum a structure constituting a thin-walled tube reappears, which is characterised by very advantageous flexural strength to mass ratio. A disadvantage of this construction is that the strip is vulnerable to damage due to loads transferred by region II shown in FIG. 1b, where the strip changes its shape from flat to cylindrical, near the drum on which it is wound. Under a load applied to the strip in this region, damage can occur easily. This problem can be solved easily in the case of loads acting in perpendicular to the curled strip tube's axis. The most typical solution is an application of an additional stiffening in the form of a sliding ring or rollers through which the strip passes. However, such solution does not provide protection against loads acting along the tube's axis.
Documents U.S. Pat. No. 4,154,310A and U.S. Pat. No. 4,108,258A disclose drilling systems, wherein curled tubes for attenuation of vibrations and as casing have been applied.
A significant portion of the drilling system's mass is due to the head pressing system, which has to be long, stiff and allow to transfer heavy loads, in the range of 100 N to 500 N. Such loads acting along the axis of the wellbore exceed the durability of typical curled strip constructions. It is commonly known to those skilled in the art, that curled strip tubes subjected to such loads become damaged in the transition region.